The published literature includes a multitude of designs for stent delivery catheters that will deploy a self-expanding stent, such as one made out of nickel titanium shape memory alloy, at a site of stenting within the human body. For deployment, a sheath that surrounds the stent and confines it radially is pulled proximally, relative to the stent, by a so-called “pull wire”. Such a pull wire invariably lies within a lumen running lengthwise along the shaft of the catheter, all the way back to a hand unit at the proximal end of the catheter, where it can be pulled, to pull back the sheath. Typically, there is an annular member at the proximal end of the sheath, that is slidable on the catheter shaft, and which is fixed in relation to the proximal end of the sheath and the distal end of the pull wire. Pulling on the pull wire pulls the annular component proximally on the catheter shaft and this in tum pulls the sheath proximally relative to the stent that lies around the shaft, distal of the annular element.
It is well known that the act of putting tension on the sheath that surrounds a self-expanding stent, in order progressively to deploy the stent, can have the effect of pulling the stent proximally. Unless this tendency is controlled and restricted, if not prevented, then there is a risk that the stent will be pulled proximally relative to the location in the bodily lumen where it is to be deployed. Obviously, deployment proximal of the intended deployment location is undesirable. There have been various proposals, how to minimise the extent of such proximal movement of the stent. One proposal, see Applicant's W02003/003944, is to establish within the catheter shaft a continuous strand of metal that runs all the way from the hand unit to a pusher ring that abuts the stent and so can resist proximal movement of the stent, when the sheath around the stent is pulled back proximally. However, the present inventors have determined that, even with a continuous metal strand resisting proximal movement of the stent, there is still a residual possibility that the stent will end up being placed at a location proximal of the desired location, and it is one object of the present invention to further minimise the chances of this adverse event occurring.